Sialuria: Ninth Patient Described Has a Novel Mutation in GNE

Hereditary thrombocytopenia with platelet sialic acid deficiency and mutations in the GNE genes

BACKGROUND

The inherited macrothrombocytopenias are rare disorders and the underlying cause can be identified in many cases but in some, this can remain enigmatic. Platelet transfusions are often administered during hemorrhagic events.

METHODS

A patient with previously unexplained inherited macrothrombocytopenia with a platelet count between 3-20 × 10⁹ /L is described in which studies were performed using exome sequencing (ES) and platelet flow cytometry.

RESULTS

Both the hemoglobin and white cell counts were normal. ES revealed two suspicious variants, one likely pathogenic and one a variant of uncertain significance, in the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene, and flow cytometry showed diminished expression of surface platelet sialic acid (about 5%) but normal red cell sialic acid. The Thrombopoietin (TPO) level was low, and the patient responded to TPO-mimetic treatment with an increase in the platelet count.

CONCLUSION

Two variants in the GNE gene were able to be upgraded to pathogenic with apparently restricted expression to the megakaryocyte lineage. Platelet transfusion may be avoided in these patients with TPO-mimetic treatment.

Free urinary sialic acid levels may be elevated in patients with pneumococcal sepsis

OBJECTIVES

Urine free sialic acid (UFSA) is an important diagnostic biomarker for sialuria (GNE variants) and infantile sialic acid storage disease/Salla disease (SLC17A5 variants). Traditionally, UFSA has been measured using specific single-plex methodology in relatively small cohorts of patients with clinical symptoms suggestive of these disorders. The use of multiplex tandem mass spectrometry urine screening (UMSMS) has meant that UFSA can be measured semi-quantitatively in a much larger cohort of patients being investigated for suspected metabolic disorders. We hypothesised that the neuraminidase of Streptococcus pneumoniae may release free sialic acid from endogenous sialylated glycoconjugates and result in increased UFSA levels.

METHODS

We conducted a retrospective review of clinical records of patients who were identified as having S. pneumoniae infection and who also had UMSMS at the time of their acute infection.

RESULTS

We identified three cases of increased UFSA detected by UMSMS screening that were secondary to S. pneumoniae sepsis. Additional testing ruled out genetic causes of increased UFSA in the first patient. All three patients had overwhelming sepsis with multiorgan dysfunction which was fatal. Glycosylation abnormalities consistent with the removal of sialic acid were demonstrated in serum transferrin patterns in one patient.

CONCLUSIONS

We have demonstrated in a retrospective cohort that elevation of UFSA levels have been observed in cases of S. pneumoniae sepsis. This expands our knowledge of UFSA as a biomarker in human disease. This research demonstrates that infection with organisms with neuraminidase activity should be considered in patients with unexplained increases in UFSA.

Sialuria-Related Intellectual Disability in Children and Adolescent of Pakistan: Tenth Patient Described has a Novel Mutation in the GNE Gene

BACKGROUND

Sialuria is a rare inborn error of metabolism caused by excessive synthesis of sialic acid due to the mutation in the binding site of the cytidine monophosphate-sialic acid of UDPGlcNAc 2-Epimerase/ManNAc Kinase (GNE/MNK).

OBJECTIVE

This is the first study investigating the molecular basis of neuronal disorders exhibiting sialuria in Pakistani children/adolescents.

METHODS

The current study genotyped GNE SNPs rs121908621, rs121908622 and rs121908623 by using PCR, RFLP, and DNA sequencing methods. Socioeconomic and clinical histories were also recorded.

RESULTS

Our data suggest that clinical symptoms and financial status play a significant role in conferring sialuria related Intellectual Disability (ID). SNP: rs121908623 showed G/A substitution (R263Q) in the GNE gene.

CONCLUSION

We have identified one case study in Pakistan, so this makes our research a leap forward towards the identification of the 10th case study worldwide.